Method of regenerating ion exchange resins

ABSTRACT

An improved process for regenerating ion exchange resin, includes a regeneration step of displacing captured ions from the resin to regenerate its ion-capture functionality, followed by one or more fluid-employing post-regeneration steps such as a fluid displacement or rinse, a fluid transporting or mixing, and a rinse down to quality. To avoid problems of early leakage of weakly held ions such as boron, the post-chemical or postdisplacement steps use water that is essentially free of boron, or otherwise avoid localized contamination in the regenerated resin which is used in bottles or beds ( 30 ). A two-stage polish may be operated with modified lead/lag bottles. A detector (D) for an indicator condition (conductivity, silica breakthrough) between stages determines when to shift the lag bottle forward, and periodically both bottles are replaced.

This application is a divisional of co-pending U.S. patent applicationSer. No. 10/580,865 filed 6 Jul. 2005, now U.S. Pat. No. 8,177,981,which is a National Stage application under 35 USC 371 ofPCTAJS03/II583, filed 14 Apr. 2003, which claims benefit of priorityunder 35 USC 119(e) from provisional U.S. application 60/372,206, filed12 Apr. 2002.

This invention relates to water purification and to ion exchange media.

It also relates to methods for regenerating exchange media for use inproviding ultrapure water for semiconductor fabrication or otherprocesses requiring product water substantially free of impurities.

It also relates to production of ultra pure water (UPW), and to sensing,control and maintenance in a water processing system that relies upon ameasurement, such as a measurement of conductivity or the concentrationof species in the feed or product stream, as an indicator or controlparameter.

BACKGROUND

Many processes, such as semiconductor fabrication processes, requirewater to have an extremely low concentration of ionic and non-ionicimpurities. A manufacturing or processing facility with suchrequirements generally establishes a dedicated water purification planthaving suitable treatment capacity and impurity removal characteristicsto meet its process requirements. Such a treatment plant typicallyincludes a number of different treatment stages specially selected andarranged to be effective with the particular feed stream received from alocal supply, such as a municipal water system, a surface water, aground water well, treated wastewater or a combination of such sources.When the feed supply is received by the end-user, e.g., by asemiconductor water plant, the in-plant treatment of the resulting feedstream achieves a higher degree of purity by processes such as waterfiltration, conditioning such as softening or pH adjustment, anddeionization, demineralization, degasification or other impurity removaltreatments. One common initial treatment is to pass the feed throughreverse osmosis (RO) membranes, or through ion exchange beds. Highlevels of deionization are typically achieved by passing the waterthrough units such as electrodialysis (ED) or electrodeionization (EDI)devices, and distillation may be used in some applications. Organiccompounds may pass unaffected through some treatments, or may beintroduced or reintroduced by organisms that colonize conduits and tanksin the system. Often these are addressed at one or more stages oftreatment steps such as microfiltration, capture in activated carbon orother media, and by breakdown with ultraviolet energy or oxidation. Thebreakdown or oxidation products may be removed by one or more of theother processes described above.

An in-plant high purity water system may present design problems ofvarious types. The plant must initially be designed to address the rangeof anticipated feed waters and dependably achieve the minimal requiredlevel of water quality. Beyond the factors of capital cost and operatingexpenses, and the environmental considerations raised by the volume ofwaste water and by-product of the contaminant-removal treatmentprocesses, various unanticipated problems may arise. Types or levels ofcontaminants in the feed water may change abruptly, necessitatingchanges in treatment protocols. The periodically-performed process ofregenerating an ion exchange bed, or the unanticipated fouling in thetreatment line of a bed or membrane-based treatment system (an RO, ED orEDI unit), may destabilize or impair the treatment process or thequality of the output stream. One therefore seeks to detect problems ofthis type by the use of diverse monitoring instruments, such as aconductance meters or total organic carbon (TOC) monitors on the outputstream or instrumentation elsewhere in the system, and suitablemeasurements such as off-line ICP-MS measurements. These are applied todevelop or maintain robust or effective operating and maintenanceprocedures. Even so, the continual introduction of new fabricationtechnologies requires plant operators to frequently ascertain whetherexisting water quality specs remain sufficient.

Because the normal output water of a high purity treatment plant hassuch low levels of contaminants, the appearance of an unusual tracecontaminant may go undetected when the overall level of the class ofcontaminants, such as TOC, or other parameter, such as conductance,appears to remain within generally accepted levels. Indeed, anunrecognized or unexpected contaminant might impair the response of thedetector, rather than simply passing undetected. In such a case,observation of variation in a process parameter (such as the stabilityor sensitivity of lithographic exposure or development) or a decrease inquality of a manufactured product (observed, e.g., as an increase innumber of defects in a semiconductor wafer) may provide the firstindication that the product water has experienced a detrimental change.In this case, investigation is needed to identify the responsiblecontaminant or treatment unit, and to develop procedures that will, inthe future, prevent such quality deviations or detect the responsibleagent before it affects the production line. Production down time isquite costly, and the observation of unexplained defects or processvariations raises the possibility of additional undetected latentdefects, and the specter of defective manufactured products further downthe manufacturing train.

Focusing on just one impurity relevant to the present invention, it isgenerally thought that the presence of boron in UPW product water of asemiconductor fab plant will impair a number of semiconductor processesunless its presence is specifically addressed (for example by effectivereduction of the boron load, if necessary, in a first stage, and by useof boron-scavenging resin, ion exchange bottles or other special boronremoval unit in a polish loop.) Some fab plants have therefore adopted aconservative approach, removing boron to a very low level, for exampleby a boron-selective resin column or bed, as shown, for example, in U.S.Pat. No. 5,833,846.

Other ions must also be controlled to below trace concentrations. Forthis purpose it is common to have a number of exchange resin bottles ortanks in a polish stage of the primary make up water treatment line.Because the ionic concentrations in the final stage are already quitelow, the resin can last for an extended period before exhaustion. Aconductivity monitor can be positioned after the polisher to provide aprompt indication when the resin approaches exhaustion. When the resinbecomes exhausted, ions start to break through, and this condition maybe detected by the onset of an increase in conductivity of the productwater. A silica detector may also be used to detect the onset of resinbreakthrough.

At this stage, it is common practice to send out polish stage ionexchange bottles for regeneration of their resin.

Fab plants typically also have a final polish loop for the UPW waterproduced by the primary make-up treatment line that has been stored in atank, to effect final polishing just before the water is pumped out tothe various plant processes. Since this final polish loop deals withwater that is already substantially deionized, the exchange resin bedsor bottles see only small amounts of contaminants and may last for anextended time, e.g., several years, before breakthrough or exhaustion ofthe resin occurs. These bottles are often replaced with virgin resin,rather than regenerating the resin. Since the simple act of attaching afresh bottle into the loop, or performing any conduit connections, risksintroducing some contaminants into the final loop, it is desirable tocarry out such replacements carefully, and as infrequently as possible.

For the polish stages of the primary make up treatment line, the resinsare usually regenerated. However, problems may be encountered at thisstage. Resin regeneration facilities deal with large quantities of mixedresins from diverse sources. Spent resin from mixed bottles or beds mustbe separated into anion and cation exchange resins before regeneration,and the separation processes, typically relying on fluidized settlingseparation properties affected by density, bead size and the like arenecessarily imperfect. There is thus a possibility of introducingunanticipated contamination from other resins during various regen resinhandling plant operations, e.g., conglomeration, separation by type,regeneration, rinsing, re-mixing and bottle filling. Regeneration of fabplant resins should therefore be performed by a facility that canobserve special precautions in the handling of such resins, and theregen process should be tightly controlled or specified. Often, plantswill have only one qualified vendor. Larger fab plants may perform theirown regeneration, while some fab plants may simply require thatexhausted beds be replaced with entirely new, rather than regenerated,resin.

Boron is a weakly bound ion. In operation, ions captured by ion exchangefrom product water in an exchange bed bind to the exchange resin, andweak ions may be displaced by other ions having a stronger affinity forthe resin. The more weakly held ions are therefore continuouslydisplaced and shifted toward the downstream end of the ion exchange bedas the upstream end becomes more saturated. The more weakly dissociatedspecies are also captured with lower efficiency, and may extenddiffusely along a relatively long depth of the ion exchange bed. Boron,in particular, has a non-self-sharpening wave front and moves throughthe bed well ahead of other ions. Silica, a common and weakly held ion,has recently been regarded as a good breakthrough indicator of bedexhaustion, and it may be easily detected, for example by acolorimetric, wet chemistry silica detector. The above-notedconductivity rise has also generally been considered an effectiveindicator of impending breakthrough, and can be detected by a commonresistance meter placed downstream of the polisher.

It should also be noted that some fab plants have specified a zerodetectable boron standard for their process water. This has lead to thepresence of boron being addressed by various approaches, such as thereplacement of the polish bed whenever boron concentration reached thedetection threshold. One group has reported, however, that the lattermethod resulted in the need for extremely frequent regeneration of thepolish bed—over one hundred times per year. They proposed instead anapproach of using of a boron-selective capture resin at various placesin the treatment stream ahead of the polish bed to reduce the boron loadon that unit.

Recently, it has been noted that a boron breakthrough may be detectedearlier than the silicon breakthrough, and before a detectableconductivity rise. For this purpose, boron concentration is monitoreddirectly, using a sufficiently sensitive boron detection instrument. Theappearance of boron in treated fab product water may then be used as anindicator of impending exhaustion of the polishing bed exchange resin.Boron is displaced earlier, preceding the breakthrough of silica, and assuch constitutes an indicator that may allow a more accuratedetermination of, or at least an earlier, hence more secure anticipationof, the exhaustion of a normally-functioning ion exchange bed. For suchspecialized boron detection, one instrument maker (Sievers Instruments,Inc. of Boulder, Colo.) has developed a very sensitive boron detectioninstrument for UPW monitoring and treatment process control. That boronmonitor, which is described in published International PatentApplication WO 02/12129, now permits the detection of boronconcentration at very low levels, e.g., at parts-per-trillion (ppt)concentration levels. That international patent application is herebyincorporated herein by reference in its entirety.

Boron concentration measurements made with such a detector may inprinciple be used to anticipate bed exhaustion and to determine timelymaintenance, such as replacement or regeneration, of ion exchange beds,thus avoiding unanticipated deterioration of product water quality orcostly shut-down of the water production. The detection should permitone to schedule bed replacement or regeneration well before theoccurrence of leakage of silica, or of other more tightly bound and moredestructive ions, through the polish unit in the product water.

However, boron is a loosely bound ion. If one is controlling based upona very low detection threshold, it is important that the level or shapeof the boron concentration curve be discerned, distinct from background.As noted above, it is also generally accepted that the absolute level ofboron should be relatively low. However, early measurements with asensitive detector have uncovered great variations in the boron-passingor release characteristics in a UPW product water polish stage. Boron isloosely held, is easily displaced, and is captured with fairly lowefficiency by the remaining downstream resin. An aged resin bottle,which has already accumulated a load of boron ions, will release boronions in proportion to the total ionic load as it nears exhaustion,increase the residual level of boron when the water temperature rises afew degrees. More significantly, applicants have observed that sometimesnewly-regenerated resins appear to release a large amount of boron. Itappears therefore that at least some regeneration processes do notproduce regenerated resin capable of sustained and dependable boronremoval.

It would therefore be desirable to provide a regenerated resin havinglower passing or release characteristics, and/or more effective andlong-lasting capture characteristics

It would also be desirable to provide an improved resin regenerationprocess that dependably produces regenerated resin having lower boronpassing or release characteristics, or more effective and long-lastingboron capture characteristics.

It would also be desirable to provide an improved process for producinglow-boron UPW product water.

SUMMARY OF THE INVENTION

One or more of the above desirable ends are achieved in accordance withone aspect of the present invention, by a process for regenerating aspent or at least partially exhausted ion exchange resin that dependablyproduces a regenerated and substantially boron-free resin. Theregenerated resin, when returned to a polish unit, provides anessentially boron-free product water for a substantial time until theresin becomes highly loaded and approaches exhaustion. The resin isprocessed with at least one regeneration step, such as a caustictreatment for the anion resin, to displace ionic species from theexhausted anion resin and convert ion exchange sites to hydroxyl form.The resin processing further involves one or more fluid-contactpost-regen steps, such as rinsedown, fluidized transport or wet mixingsteps. In accordance with a principal aspect of the invention, thefluid-contact post-regen steps are performed with boron-free water,and/or are performed in a manner that avoids exchange of hydroxide ionsfrom regenerated anion exchange resin with ions from any ambient fluid,and which preferable avoids exchange of hydrogen (hydronium) ions fromany regenerated cation exchange resins with cations from ambient fluid.In as much as hydrogen form cation resin can sorb weak acids, such asboric, silicic, carbonic and carboxylic acids in equilibrium withambient fluid, and hydroxide form anion exchange resin can similarlysorb weak bases such as ammonia, urea and amines, it is preferable thatfluids coming into final contact with such regenerated resins besubstantially free of such weak acids and weak bases, respectively, andpreferably completely free as measured by any relevant analyticaltechnique. Post-regen steps should also avoid incorporating orphan resinparticles in the separated resins—that is, anion exchange particles inthe resin intended to be exclusively cation exchange particles andcation exchange particles in the resin intended to be exclusively anionexchange particles. Such steps should also be carried out to avoidincorporating non-regenerated resin particles of any type.

In accordance with another aspect of the invention, a water treatmentplant is operated to produce pure water for use in regeneration andparticularly for any post-regen steps—rinsing, final rinsing, resinmixing, resin transport and any other unit operations requiring fluidcontact in the overall regeneration procedure. The treatment plantincludes and provides a boron-free water output. As noted above, suchoutput is preferably free of all weakly ionizable acids and bases, aswell as their ionization products; that is, such output is intrinsicwater. For example, the product water stream may pass through variouspurification unit operations followed by one or more polish unitoperations intended to produce a stream of water that is essentially orsubstantially intrinsic. The product stream may, for example, be sent toone or more tanks or reservoirs for later use in regeneration andpost-regeneration steps. The product water may be segregated among suchtanks according to the quality of water actually obtained, and the bestquality water used for more critical operations. The materials ofconstruction of the tanks and conduits are selected to avoidcontamination of the substantially intrinsic product water (for examplea high quality PVDF) and the stored water is protected from ambient aircontaminants such as carbon dioxide or microorganisms. Alternatively, oradditionally, treated product water from such a tank may pass through afinal polish loop with one or more polishing unit operations, such as UVtreatment and electrodeionization, and may circulate to points of use ina regen plant, and/or to a regen room in a fab or other plant, withexcess water being returned to the tank(s). The intrinsic water streamis monitored for boron concentration (e.g., boric acid) at one or morepoints, preferably at least at a position after the polisher or thefinal polisher, using a sensitive (preferably sub ppb) detector.Preferably the stream is also monitored, as applicable, for conductivityand other (non-boron) undesirable species, e.g., TOC, silica, inorganiccarbon, urea, ammonia, amines or the like. The intrinsic watercirculation or delivery to the intrinsic water tank may be suspended ordiverted when a detection threshold concentration is exceeded, so thatthe water for regeneration processing remains free of boron and a supplyof intrinsic water is thus assured for use in regeneration andpost-regen rinse and other fluid processes. When this water is used incritical regen and post-regen unit operations, the resins areregenerated without picking up fresh boron or other undesirablecontaminants which could elute quickly or unpredictably in service.Separate or mixed beds containing resins regenerated and post-treated inaccordance with this invention using intrinsic water, however, producewater having a stable and low content of boron and/or such othercontaminants.

It is preferred that the separate or mixed beds employ solely resin thathas been treated in accordance with the invention. However in otherembodiments, only resin in a downstream portion of the bed or beds maybe so treated. In that case, any leakage from or through upstreamportions is sorbed by the downstream portion(s). It has been found,however, that if an upstream portion of the bed is or has beencontaminated by boron or other weakly held species, such species willmarch down the bed, even if the feed to the bed is intrinsic water. Thisphenomenon may be attributed to constant re-equilibration of weakly heldspecies with flowing ambient water.

A water treatment system of the invention may employ a bed ofboron-scavenging resin, such as boron chelating anion exchange resinsbased on glucamine or the like, and/or aggressively regenerated strongbase anion exchange resin to substantially remove boron. Preferably oneor more detectors monitor boron at relevant locations in the treatmentsystem, e.g., samples water downstream or upstream of the resin bed, ora probe samples within the resin bed, for example toward a downstreamend thereof or at the output of the upstream stage of a two-stagepolisher. By sampling at least one point ahead of the final outlet, thedetector is able to determine a profile of the remaining resin activity,and deduce the condition of the bed or the output quality of watertreated by the bed, earlier or more accurately. By sampling upstream ofthe bed, one may determine a time/flow profile of remaining treatmentcapacity, may implement a predictive model of the boron uptake forscheduling resin replacement or regeneration, and may predict the outputwater quality and its suitability for different end uses.

One embodiment of a UPW treatment system, or a treatment system used toprovide intrinsic water for regeneration and/or post treatment of resin,may employ an ion exchange unit comprising an upstream resin bottle orcontactor unit and a downstream resin bottle or contactor unit, with oneor more detectors, such as a silica detector, a urea detector, aconductivity detector or a boron detector, positioned between the units.Based on detection of a threshold, or an actual or anticipatedbreakthrough, the upstream unit is removed for regeneration, while thedownstream unit is moved to the upstream position and a new orregenerated bottle is placed in the downstream position. With thislead/lag arrangement, the downstream position is largely shielded fromthe major ionic load, and experiences only a low level of displacedweakly bound ions; it thereby provides a substantially full ion exchangecapacity when moved to the upstream position, with only a slight initialionic loading that is, moreover, largely comprised of weakly ionicspecies such as boron and silica, concentrated at its upstream end.Thus, in upstream service it will capture all strongly bound ions, andrecapture substantially all weakly bound ions displaced by the stronglybound ions, passing only a slightly higher residual level of weak ions.When the detector again detects impending exhaustion of the upstreambed, the upstream bottles are again sent out, and the downstream unit(s)moved forward and replaced by new units. At regular intervals, forexample at every third silica or conductivity breakthrough of theupstream bottle, both bottles may be sent out for regeneration. Thismodified lead/lag procedure assures that, at no point does the currentdownstream bottle possess a distribution of weak ions that would bleedat an unacceptable level into product water. While such bed rotation hasbeen described in terms of two resin contactor units, more units may beused, for example in a “carousel” arrangement.

It will be seen that in principal according to this invention, in an ionexchange resin regeneration facility making regenerated resin intendedto produce essentially intrinsic water, part of the resin so regeneratedmay be diverted to furnish the intrinsic water for the resinregeneration processes. In order to minimize the amount of resin neededfor this water supply, it is preferable that the water be extensivelypretreated by unit operations of known type so that it is substantiallyfree of TOC and minerals. Also, while the invention is described largelywith specific reference to removal of boron to below a threshold thathas become critical for semiconductor fabrication, the inventionapplies, with corresponding changes, to any and all contaminants thatare weakly bound by such resins, including silica, carbonic acid, urea,ammonia, amines, carboxylic acids and so-called “pseudo-salts” such asmercuric chloride or mercuric cyanide. These may for example belong to aclass of at least slightly soluble uncharged weakly dissociated (orstrongly coordinated) coordination compounds, which share some treatmentproperties with weakly dissociated acids and bases. Since many watersources are contaminated by industrial and agricultural effluents, andfab plant processes may be susceptible to ppt-levels of contaminantthese weakly ionized or uncharged coordination compounds must be watchedcarefully.

BRIEF DESCRIPTION OF DRAWINGS

These and other features of the invention will be understood from thedescription and claims herein, taken together with the drawings ofrepresentative embodiments and illustrative details thereof, wherein:

FIG. 1 is a schematic representation of a UPW treatment plant of theprior art and of the present invention;

FIGS. 2 and 2A illustrate an ion exchange resin bottle and evolving iondistributions in the resin;

FIG. 3 illustrates a resin regeneration process in accordance with oneaspect of the present invention;

FIG. 4 illustrates UPW plant operation in accordance with another aspectof the invention;

FIG. 4A illustrates resin contamination during regeneration; and

FIGS. 4A and 4B illustrate a separation device according to anotheraspect of the invention for addressing the contamination of FIG. 4A.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a water treatment plant 100, which maybe conveniently viewed as a sequence of treatment or conditioningprocesses (not separately identified in the FIGURE) some in series andsome in parallel that perform a pretreatment 10 followed by furthertreatment 20 to produce a product water substantially free ofimpurities, i.e., intrinsic water. The exact unit operations intreatment processes 10 and 20 may vary widely, depending upon thequality of the starting water or feed stream, and the desired quantity(recovery) and qualities of the high purity treated water, i.e., theproduct stream.

The pretreatment 10 may include processes that are carried out upstreamin the supply, such as settling, flocculation and filtration to renderthe water suitable for later treatment stages, as well as processes suchas sterilization, softening, pH adjustment or the like which may serveto address specific impurities or to enhance the stability, yield oroperation of the pretreatment or of the later stages. Typically suchtreatment (e.g., municipal treatment) removes a major portion ofsuspended solids and microorganisms, and may reduce or change the ionicload when unit operations such as coagulation and microfiltration areapplied upstream. At a fab plant or regen facility, the pretreatmentstage may include any of the above processes if the source is local, andmay further include (generally finer) filtration, as well as operationsto address species, specific contaminants or pH conditions including anyintroduced earlier by the upstream treatments or processes.

The treatment stage 20 may also involve a number of different processes.For example in a semiconductor primary make-up water plant, the in-planttreatment of the resulting feed stream achieves a higher degree ofpurity by various processes of finer filtration (e.g., by dead endcartridge filters, dead-end or cross-flow microfiltration orultrafiltration, or precoat filters), deionization/demineralization(e.g., by ED, EDI, RO or nanofiltration, ion exchange beds ordistillation), sterilization and degasification of the water.Scale-forming and other electrolytes, large molecules and a substantialportion of the ionic load may be removed by reverse osmosis (RO)membranes, while high levels of deionization or demineralization aretypically achieved by passing the water through units such aselectrodialysis or electrodeionization units and/or ion exchange beds.Residual levels of organic carbon compounds are often addressed by oneor more steps such as capture in activated carbon or other beds, andbreakdown with ultraviolet radiation or ozone, possibly preceding orfollowing one or more of the above-listed impurity removal units thatare effective for removing smaller molecules and ions produced by theseprocesses. In some parts of the world, it is common to have a number ofion exchange resin beds constitute the major front-end treatment—e.g., acation exchange bed, an anion exchange bed, and a mixed ion exchange bedfor demineralizing the feed. In systems for producing suitably purewater various known combinations of oxidizers (e.g., catalytic andphotolytic) and sorbers or filters may also be used to address organicsand certain protected or poorly ionized or less soluble components.

In accordance with one aspect of the present invention, the high puritytreatment stage includes a polish stage 22 in which residual impuritiesare removed. Polish stage 22 may be physically located at an output endof a sequence of treatment units so that it treats the water fromupstream treatment operations. It may alternatively or additionally belocated at the downstream end of a second or intermediate treatmentsegment of a multi-stage treatment plant. Typically, final polish unitoperations (not shown) are also provided, e.g., downstream of polish 22or in a portion of the plant that receives or uses water that previouslypassed through the polish 22, to polish water entering the plant's mainUPW distribution network.

As noted above, such a final polish typically involves large capacitybeds or a number of bottles, and is generally replaced with new resinwhen it becomes exhausted. However, the resins of polish stage 22 aretypically replaced more frequently, and for this purpose, freshregenerated resin is substituted when water quality drops or is expectedto suffer. Stage 22 includes one or more exchange units, typically inthe form of mixed ion exchange resin beds or bottles, of which onebottle 30 is schematically illustrated in cross section in FIG. 2. Mixedresin from such beds or bottles is preferably regenerated at a separateregeneration facility, which may be part of the same plant (for a largesemiconductor fabricator) or may be an offsite independent resinreprocessing facility, rather than regenerated in situ.

As shown in FIG. 2, resin bottle 30 has a water inlet 32 at its proximalend 31 through which inlet water to be treated enters and permeatesdownwardly through an impurity capture medium 35, e.g., a mixed bed ofion exchange resin beads, which capture the remaining impurities as thewater flows toward the distal end 33 of the bottle. Various screens,filters or seals (not shown) assure that the capture medium, e.g., thebeads of exchange resin, remain in the bottle. At end 33, an opening 34a in a weir-like collector plate 34 b (shown partially cut away) acts asan exit port, blocking loss of beads while permitting the polished waterat the distal vessel end 33 to enter the exit pipe 34 c, whence it flowsback up within the column of resin 35, connecting to an outlet 36 at theproximal end 31 of the bottle. Thus, in the configuration shown, waterflows unidirectionally through the resin bed, from the top of bottle 30downward, becoming progressively purified by contact with the medium,resin 35. Correspondingly, the column of resin 35 in the bottle becomesprogressively mineralized, or spent, over the course of its useful life,from the top down as it captures impurities from the inlet water. Bottle30 may be oriented in any direction, and the terms “top” or “top down”are intended only to refer to the inlet end, or the inlet-to-outletdirection.

The overall course of medium activity and state of the medium bed overtime is illustrated schematically in FIG. 2A, using ion exchange resinas an example of the capture medium. At time t=0 the resin is in asubstantially completely regenerated state. Later, at time t=1corresponding to a relatively fresh resin state, for example after about5-10% of its useful duty life, a relatively shallow layer of resin nearthe inlet end 31 has captured ions from the treated water. The latterinclude both strongly bound ions and weakly bound ions. At this stagethe resin below the capture zone remains strongly active and itsfunctional exchange sites remain substantially in the hydrogen and thehydroxide forms, respectively. The resin in the capture zone itself maystill possess substantial amount of anion exchange sites in thehydroxide state.

As further shown in FIG. 2A, at a later time t=2, the depth of the resinbed that has been substantially taken up by captured ions extends moredeeply and the cumulative load of strongly bound ions has increased. Theresin at the proximal end has many or most of its ion exchange groupsoccupied, and arriving strongly bound ions compete with, and displace,the already-captured but weakly bound species. The latter move furtherdownstream, and are largely re-captured downstream by the essentiallyfully-regenerated resin. The effectiveness of this capture is weak,however, so that the weaker ions are taken up over a relatively longdownstream plume. Thus, the resin bed 35 then has a longer “capture”zone, the composition of which is graded from a well-definedself-sharpening band upstream comprising predominantly strongly boundions, to a diffuse (non-self-sharpening) region downstream thereofconsisting predominantly of weakly bound ions. At such time t=2, asubstantial portion (R) of the bed height still remains substantiallyfully regenerated, still quite effective at stripping residual ions fromthe water coming from upstream. For example, in the case of a bottlefive feet in length, the region R may extend more than two feet alongthe downstream end of the flow path. Since strong ions are capturedquite quickly, and even weak ions may be captured at a rate to effect asignificant reduction in load (e.g., a 2 log reduction per 50 mm oftravel through the fresh resin), all ions are still captured and remainwithin the bottle. The resin bottle functions properly.

The third panel of FIG. 2A shows the situation at a later time t=3. Atthis time, the total bed burden of removed minerals is quite large. Thestrongly bound ions have displaced weakly bound species toward thedistal outlet 34 a (FIG. 2), and the weakly ionic species such assilicic and boric acid, urea, amines now reside in a band broadlydistributed downstream of the sharply define capture band comprisingstrongly bound ions. In actual operation, the bands are not clearlydelineated; each involves a distribution tapering in concentration orextending into an adjacent region. Further, at such time t=3 the lengthR of the resin that remains substantially completely regenerated hasbecome quite small, extending for perhaps only a few inches upstream ofthe outlet 34 a. For many feed waters and treatment systems, the boron(boric acid) region may extend downstream of the silica (silicic acid)region and thus constitute an earlier breakthrough or quality-affectingevent. As upstream resin exhaustion becomes more intensive andextensive, the remaining length R of strongly active resin may be ableto trap/capture only a small fraction of the weakly bound ions reachingit. Weakly bound ions may then leak out, and the electrical conductivityof the effluent may thereafter start to rise detectably. Moreover, boronpassage at t=3 (and potentially the other weakly bound species) mayalready increasing; A sensitive boron detector as described in theaforementioned international patent application may detect the increasedboron concentration in the output, providing an indication that theexchange resin should be replaced or regenerated. Thus, the bottle maybe taken out of service and its resin may be regenerated or replaced atthis time rather than relying on the conventional, later, conductivityincrease or silica breakthrough monitoring to determine when resinbottles are to be regenerated.

When regeneration of the exchange resin in the prior art is carried outafter removing the resin from the bottle, typically the resin from manybottles, columns or beds is consolidated as a batch for regeneration.Mixed resins are first separated, e.g. by a hydraulic separationtechnique that relies upon the different settling rates in a flowingfluid (as determined by the differing particle densities, fluid densityand other factors), or when such separation is not feasible, byadditional techniques such as screening. The anion resins and cationresins so separated are regenerated separately. The anion exchange resinis regenerated by placing the resin in a bed and flowing very purecaustic (e.g., at a 4-8% concentration) through the resin bed to stripaccumulated ionic loading and return at least the upstream portion to asubstantially complete hydroxide form. The caustic remaining in theupstream portion is then driven downstream and removed, e.g., byphysically driving the caustic solution out of the tank or regenerationvessel using a flow of intrinsic water. The caustic thereby contributesto the complete regeneration of the downstream resin. This regenerationstep may be repeated one or more times, and this may be done inconjunction with one or more displacement or conversion (colloquially“salt squeeze”) steps to enhance the effectiveness for removing one ormore specific components of the ionic burden in the bed. The regeneratedresin may the be rinsed down for an extended period, which may be aslong as twenty four hours, until the rinse water has an acceptably lowlevel of boron, or conductivity, or silica, TOC or other contaminants.Part of the rinse water may be recycled, with or without purification(e.g., by ED or EDI) to make up regenerant solution and initial rinses.In various known processes, if the resin is to be returned to a resinbottle, the regenerated resin is then loaded by flowing it in a liquidslurry or suspension into the bottle. When a mixed bed/bottle isdesired, the regenerated resins may be mixed and then loaded into abottle, or loaded and then uniformly intermixed. Mixing may beaccomplished by applying a sparged bubbling or pulses of gas in ashallowly-covered bed of anion and cation exchange resin beads. Thepulsatile regimen causes the different resins to become wellinterspersed. Thus, the regeneration steps involve much contact withwater for operation of caustic displacement, rinsing, particle transportand mixing steps. Similar procedures should be used to thoroughlyregenerate cation exchangers, e.g., using very pure sulfuric,hydrochloric or other acid instead of caustic.

In addition to or as an alternative to regeneration with pure caustic orpure acid, respectively, other regeneration methods have been proposedand may be in use. One such proposal is a process of regeneration byloading the resin into an electrodialysis unit and running a flow ofdemineralized UPW water through the unit for an extended period whilethe electrodes are energized in this case the resin is regenerated andis stripped of a substantial portion of its ionic load byelectrodialysis. See, e.g., Walters et al, Industrial and EngineeringChemistry 47 (1) (January 1955). In this case the concentrationcompartments are preferably also loaded with resin to lower the stackresistance, and electrical current is passed through the stack until thecurrent efficiency, or transport of non-hydrogen, non-hydroxide ions isnot detectably different from zero. The resin may then be removed fromthe stack and loaded in a bottle or bed. In this case also, theregeneration steps as well as the post-regen transport or handling andother steps involve extensive contact with water. In the case ofelectrodialytic regeneration, hydroxide and hydrogen ions are providedby water splitting at resin or bead interfaces; other electrolyticprocesses can be applied to regenerate resin by electrolysis at adjacentelectrodes or composite membrane electrodes. See, for example,Galliland, U.S. Pat. No. 3,645,884. In accordance with a principalaspect of the present invention, water used in critical regenerationsteps should be essentially free of the problematic species in the aboveexample, boron—or more generally the resin processing water should beessentially intrinsic water.

In addition to separation and regeneration of resin removed from bottlestanks or other containers, in situ separation and regeneration are alsocommonly practiced. For in situ regeneration of a mixed bed, suitableseparation of the different resins is effected; for example, an upflowof fluid may be applied to the mixed bed to separate the exchange resinbeads into an upper (anion) exchange resin layer and a lower (cation)exchange resin layer, and water may then be injected between the layersto maintain separation, or a layer of neutral beads of intermediatesettling rate may be interposed to avoid creating a zone of mixed resin.A flow of caustic may then be introduced from the center upward and aflow of acid introduced from the center downward, to regenerate therespective resin layers. Once regenerated, the beads may be mixed inplace and subjected to a top-down rinse to quality. Various otherprotocols may be followed. For example pure caustic may be passedthrough both layers, regenerating the anion resin and converting thecation resin to sodium form. The cation layer may be subsequentlyregenerated with pure, strong acid. Still other protocols may involvedifferent sequences of regenerant flow between one or both ends and acentral distributor/collector. During these processes, pure water may bepassed through one half of the column to prevent intrusion of theregenerant flowing in the other half, and this water may serve as atleast part of the rinse for such resin. Once regenerated by any of theabove methods, the resins are remixed as describe above.

Some Preferred Embodiments

The discussion below is intended to encompass improvements in all suchregeneration processes, by illustration, addressing in detail forclarity of exposition, the regeneration, fluid-contact and handlingsteps of a batch regeneration process.

Briefly, applicant has found that even a newly-regenerated resin bottle30, containing resin that has been regenerated by a conventionalprocess, when it is placed in a polish stage or final polish loop asdescribed above, may release an unexpectedly high amount of undesirablecontaminant, e.g., boron. The boron concentration in water leaving thebottle 30 may be greater than that entering in the treated stream.Applying a boron detection threshold as described above to determinewhen to replace the resin bottle would then result in an unusually shortduty life, of hours or days, instead of weeks or months. Following amethodical investigation, applicant realized that this situation wascaused by the presence of inexplicably high levels of boron loading inat least some of the resin beads present in a regenerated bottle, andthat the regeneration process thus involved boron contamination.Applicant further surmised that boron-contaminated but otherwiseregenerated resin resided, at least in part, at a downstream end of thebottle where effective recapture would not be achieved and boron leakageout of the bottle would thus arise. An analogous situation could applyto the other weakly bound species identified above. Furtherinvestigation resulted in a realization that one source of thecontamination resulted from contact with various rinse and other watersduring the regeneration processing, and was exacerbated by localizedenrichment processes and subsequent bead dispersal processes governed atleast in part by the positioning and movement of resin during handlingin the regeneration, rinsing and loading procedures.

To solve the problem of underperformance and premature breakthrough ofthe resin, applicant developed an improved regeneration process andsystem, wherein the improvement includes steps and apparatus forscrupulously controlling the undesired weakly bound entities in thewater which will come into contact with the resin during the late stagesof and after regeneration, e.g. employing substantially boron-free waterfor such contact. Such process and apparatus assure that boron is notinadvertently introduced into otherwise thoroughly regenerated resin,anion exchange, cation exchange or other. The process is applicable toaddress any and all weakly bound entities. In this regard, applicantrealized that when a water intended to be essentially intrinsic, such asthe UPW plant water, is employed for such post-regen processing water,then if that UPW plant water were produced during the time when thepolish resin bottles approached exhaustion (e.g., near time t=3 in FIG.2A when silica is about to break through or conductivity rise), theproduct stream would already have experienced elevated levels of boronfor some period of time due to displacement or other release, andnon-recapture of the downstream weak ions (FIG. 2A, t=3). The boronwould be released in proportion to the total (i.e., integrated) ionicload of the water entering the polish bed. Thus, an extensive flow ofsuch boron-laden water in the treated product stream still possessingapparently acceptable conductivity and high purity may have beenaccumulated and applied for regeneration (or other) purposes. Applicantfurther found that such water may introduce localized boron-enrichmentin the freshly-regenerated resin, especially when a large volume of suchwater is used for an extended rinse down. Upon contact to a regeneratedanion exchange resin, this boron-enriched water would lose its boronsubstantially instantaneously to a shallow surface layer of theregenerated resin bed, thus contaminating a localized layer of thesupposedly fresh resin with a significant dose of boron. During atwenty-four hour rinse down, the boron loading acquired by the upperlayer of resin would be quite high. When this regenerated butboron-contaminated resin is moved from the mixing/rinse tank intobottles, or is redistributed within the same bottle, the layer of beadsthus contaminated can shift (as discussed in regard to FIG. 4A below)and be transferred as a slug to naturally fill a substantial portion ofa bottle, or even worse, fill a portion of the distal end 33 of abottle. In that event the layer could quickly start leaking boron fromthe otherwise regenerated resin column. As the surface layer slumpsinwardly when resin is withdrawn from the regeneration tank, the resinwith enriched boron loading may be drawn off as a slug into one or morebottles while earlier- and later-filled bottles remain unaffected. Theformation of localized pockets or layers of regenerated resin that haveacquired an enriched burden of weak ions is addressed in other aspectsof the invention by techniques of resin segregation or separation duringregeneration handling.

In addition to these aspects of unintended ion loading arising from thehandling and rinse procedures, regeneration processes of the presentinvention preferably also address the possibility of “orphan” beads,that is, exhausted resin beads that fail to be regenerated eitherbecause they were left in the exhausted bottle (e.g., stuck to the wallduring the emptying process), or were positioned in a stagnant space inthe regeneration tank (e.g., in a dead-ended leg or stub, or below orbetween distributors). Great care is taken in transferring and handlingthe resin to avoid such sources of contamination.

The above circumstances are addressed and regenerated resin is preventedfrom acquiring boron loading in accordance with one aspect of theinvention by using a boron concentration detector (or more generally adetector for any of this class of problem contaminants) in the polishstage of a treatment plant to determine whether the treated output issuitable for use in regeneration processing. When the concentration ofboron starts to rise above a certain threshold (for example, one ppb),the water is stopped, or diverted or otherwise is not allowed to mixwith or pass to the UPW stream or to the supply used in regeneration.For various configurations of the invention the detection threshold maybe set at different values. For example a threshold of 70-80 ppt may beused for waters that are to be applied in quantity—such as rinse watersfor final rinse down—to regenerated resin beds.

Rather than detecting boron concentration to assure the substantialabsence of boron in the UPW product that is used for regeneration, thesuitability of the UPW product may also be assured, in accordance withanother aspect of the invention, by carrying out a polish loop operatingprocedure that always assures boron-free product. As described furtherbelow, this may be readily accomplished while reducing overallregeneration requirements by employing a staged polish unit, such as atwo-bottle staged unit. One effective operating procedure may use asimple conductivity measurement at the upstream stage to achievedependable limits on boron leakage.

FIG. 4 schematically shows such a UPW treatment system for providingproduct water for regeneration processing of resin, and operated toassure that contaminated water does not exit the treatment line. This isaccomplished by providing a capture unit, or final polish unit operationthat effects boron or other weak ion capture, and by operating the unitas described below.

The unit operations may include an upstream ion exchange bottle or stageand a downstream bottle or stage. Each of these units will typicallycomprise a single tank, or a number of bottles, e.g., about 4 to 40bottles, of resin, in proportion to the required flow volumes andtreatment line capacity; and these may, for example, be mixed resin.However, since the anion resin generally is exhausted first, thediscussion herein shall refer to anion exchange resin, or to mixed resinwith anion breakthrough occurring before cation breakthrough. Operationis as follows. Upon exhaustion of the upstream unit, the upstream unitis removed for regeneration, while the downstream unit is moved to theupstream position and a regenerated (or new) boron-free bottle is placedin the downstream position. The bottle status is detected by a detectorD. In the embodiment of FIG. 4, the detector D is placed ahead of thedownstream unit to detect exhaustion, or impending exhaustion, of theupstream bottle and determine when to shift the downstream bottleforward. With this lead/lag arrangement, the downstream position islargely shielded from the ionic loading, and thereby always provides asubstantial ion exchange capacity that prevents any significant level ofboron from leaking past it into the product water. The polish stage mayalso comprise more than two such units, for example in a carousel,wherein the respective units are successively shifted forward upon eachbreakthrough detection of a front unit.

The invention may be implemented with different detectors and operatingprotocols.

When the detector D is a simple conductivity detector, then the upstreambottle may have started shedding boron by the time detector D registersa change threshold; however the downstream bottle will have amplecapacity, and will effectively capture this initial boron leakage at itsupstream end. Thus, the downstream bottle will be only slightlyboron-loaded (with boron confined to the upper region of the bottle)when it is moved to the upstream position and replaced with aregenerated bottle. In this case, when the (conductivity) detector nextregisters an increase indicative of impending bottle exhaustion, boronwill have been leaking for a longer period. The downstream bottle willhave a greater loading extending diffusely toward its downstream end. Toaddress this situation, the lead/lag bottle replacement protocol ismodified by periodically replacing both bottles concurrently—forexample, at every second or third detector threshold detection. Asimilar modified lead/lag protocol with periodic replacement of bothbottles may be followed when the detector employed as detector D is asilica detector located between the bottles to indicate upstream bottleexhaustion. Alternatively, a boron detector may be employed. In thiscase, the detector may be positioned downstream of the downstreambottle, and a similar modified lead/lag protocol may be followed toprevent boron leakage in the product water. Alternatively, the detectorD may be a boron detector positioned between units as shown in FIG. 4.This is a preferred approach, since the detection is direct and does notdepend on correlated conductivity changes. In that case it may thendetect the state of the upstream bottle earlier, and no boron loadingwill occur in the downstream bottle. When using a boron detector, astrict lead/lag bottle replacement regimen (with or without periodicreplacement of both bottles) is effective to assure that no boron leaksinto the polished product water. It is also possible to employ asequence of three bottles in the process to further guard againstleakage of the downstream bottle between complete replacements.

Thus, these operating and detecting steps assure that at no point doesthe lag bottle become saturated with boron or start bleeding boron intothe product stream. The analytic determination of the replacementinterval for sending both bottles out for replacement may be made basedon cumulative effects of low-level boron release or passage fromupstream units, or the cumulative increase in baseline downstreamloading, since the last complete resin regeneration. When the borondetector is positioned between the upstream and downstream ion exchangeunits as shown in FIG. 4, then conventional lead/lag bottle replacementassures boron-free water. In embodiments wherein detector arrangementdoes permit weak ions to reach the downstream bottle, the boron problemmay also be addressed by replacing both bottles but subjecting thedownstream bottle to a lighter regeneration, thus saving regenerationcosts.

The problem of resin contamination during regeneration may also beaddressed by other steps in accordance with the present invention. Thiswill be better understood from a discussion of typical prior artregeneration processing 200 as shown in FIG. 3. At a first stage 201,resin from spent bottles or other vessels is separated into anion (AX)exchange resin and cation (CX) exchange resin. Typically, mixed resinsare compounded with different size and density for the two types,allowing the two resins to be isolated by hydraulic separation. The AXand CX resins are then loaded into separate tanks at stage 202, and theAX resin is treated with very pure caustic at stage 203 at a suitableconcentration, e.g., typically 4%-8%. The caustic treatment displaces amost if not all of the captured ions from the spent resin, as well asorganic and inorganic foulants, regenerating the resin to hydroxideform. Often the resin may contain polymeric silica, and it is thendesirable to use the caustic to accelerate depolymerization of thesilica. A substantial soak time may then be required.

The caustic is then displaced from the regeneration tank at step 204 bya flow of clean water, which may also be warm. Typically the clean waterat stage 204 is applied along the same direction as the caustic,typically from the top of the tank, pushing the caustic downwardly andout. The clean water thus contacts the fully regenerated resin, and anyminerals present in the clean regen water are immediately captured bythe upper few inches of the resin bed. Thus, at this stage, if the cleanregen water in fact possessed a boron loading (or other weakly boundspecies), the upper few inches of the resin in the tank would pick upsubstantially all of this boron or other species immediately downstreamof whatever region had been occupied by any strongly bound ions.

Washing with caustic may be performed several times, together withancillary processes, such as displacement or conversion steps thatenhance the rate or endpoint of removal of the captured ions. One ormore rinses 205 may also be applied at this stage, again with thepossibility of stripping ions from the rinse water into the upstream fewcentimeter layer of the resin in the regen tank.

The regenerated cleaned resin is then transported with fluid to a remixtank 206 and combined with regenerated CX resin. The resins at step 207are mixed in the remix tank. Typically, movement of the resin from theregen tank to the remix tank is carried out hydraulically, in a fluidflow using clean water to transport the resin. In the remix tank theresin undergoes a mixing operation 207 to uniformly intersperse thedifferent AX, CX resins. This mixing is also a fluid-contactingoperation, and is typically effected by blowing down the water level toabout an inch above the surface of the resin, and applying short burstsof inactive gas (i.e., gas free of ammonia, carbon dioxide or othercomponents that might interact with the exchange resin) upward from thebottom of the tank to agitate the resin beads without, however,permitting fluidized settling or sedimentation of the beads to occur.Once the regenerated resins have been remixed, they are rinsed down toquality in the remix tank or another tank at stage 208. This may be alengthy rinse, typically a few hours but possibly tens of hours, so thata substantial amount of ions may be captured from the rinse water, ifany are present. Typically, following rinse down, the clean regeneratedresin is next transported to bottles at a step 209. Transport to bottlesis typically performed as a flow of hydraulic slurry, and the fluid isthen blown out of the bottles at stage 210.

Thus, following caustic treatment or treatments of the anion exchangeresin with caustic, there are a number of stages where clean water andor gas contacts the resin. When this fluid is applied top-down either asa single pass or circulated flow, any ions present in the fluid maybecome captured at higher concentration in a localized (top or upstream)stratum of the resin, thereby producing a body or layer of morehighly-laden resin particles that will later shed their weak ions whenplaced in service. If this ion capture occurs before the resin is loadedin the final bottles, the contaminated beads may end up in thedownstream end of the resin bottle.

FIG. 4A illustrates this situation and its evolution during theregeneration procedure. A remix tank 300, holding by way of exampleabout fifty cubic feet (2 of regenerated resin 310, has been rinsed downfor an extended period, resulting in the formation of a layer ofenriched or ion-laden resin 311 at the top of the tank. The solid linesrepresent the situation immediately after rinse down to quality. Thatrinse down constitutes the major exposure to water in the regenerationprocessing, and thus has the greatest potential to form substantiallyenriched (contaminated) layers or pockets of resin. In FIG. 4A, a layerup to several inches deep has been formed at the surface of the bedduring step 208. As the rinsed resin is drawn from the tank into cleanresin bottles at step 209, the remaining resin slumps, as shown by thedashed line contour in FIG. 4A. The contaminated layer moves centrallyand downward, forming a plug-like or concentrated body 312,schematically shown as a dark descending whorl or vortex in theremaining resin. As is apparent in FIG. 4A, this spatially-concentratedmass of recontaminated resin may be drawn as a single mass or slug, oras several successive masses or slugs, into a bottle being refilled. Thefirst few bottles are thus filled with clean resin delivered exclusivelyfrom the bottom of the tank, while one or more of the subsequentbottles, or downstream ends of the subsequent bottles, may be filled toa substantial or even complete extent with significant amounts of therecontaminated resin 311.

The invention solves the above problem in one or more of several ways.Thus, by assuring that the water used for regeneration is sufficientlyis clean, i.e., is substantially intrinsic water, free from boron andstrongly bound as well as weakly bound entities generally, as discussedabove, applicant assures that the regenerated resin does not acquiresuch a boron-laden or recontaminated band 311, 312, and moreoverpossesses an essentially unmeasurably low loading of such entitiesthroughout. As a result, bottles or beds packed with the regeneratedresin will not have highly contaminant-laden resin loaded into ordispersed within it. Instead, they will have essentially pristine resinthroughout, and will result in a well-defined and clearly detectableresidual ion concentration in the product water that is readilyinterpretable as a bed aging curve for effecting fab plant treatmentcontrol. That is, the beds will exhibit the expected high purity wateruntil shortly before true resin exhaustion. This will allow thedetection methods described above (electrical conductivity, boronconcentration, silica concentration) to be used to determine when theeffluent water may be safely used, e.g., in a fab plant. It also allowsthe detection to predict the time when bottle regeneration orreplacement will be required. The same handling precautions allow virginresin to be dependably handled and installed without contamination.

As noted above, the common practice of processing the regenerated resinwith supposedly clean rinse or other water can lead to contamination ofupstream portions in a rinse tank when such water in fact containscontaminant species. Such contaminated portions or layers have beenfound to be a significant source of dispersed contamination under thenormal handling conditions discussed above. However, one method ofaddressing that problem in accordance with the present invention is toreload the resin in its final bottles before rinse down. This assuresthat, although the top stratum of resin in the bottle or vessel mayacquire ionic loading, the contaminated resin is not dispersed andleakage of weakly held ions will not occur until natural exhaustion incontinued use proceeds along the full depth of the bed.

In another aspect of the invention, to assure that no bottle or vesselreceives a bolus of recontaminated resin, applicant rinses in aconventional fashion, but physically separates the top stratum of rinsedresin from the remainder of the regenerated resin at this stage of theresin regeneration process, leaving only uncontaminated resin to refillbottles or vessels. In one embodiment of this aspect, this is achievedby placing a screen, perforated tray or other bead-retaining structure55 some inches below the upstream surface of the bed of regeneratedresin in a final rinse-down tank as shown in FIG. 4C. Conveniently thisstructure may be a liquid distributor. After final rinse down, resinabove the screen may be lifted out or flow-transported from the vessel.The remaining major portion of the bed is then free of contamination andmay be safely transported out the lower end of the tank into bottles orother vessels. The possibly contaminated upper portion that is removedmay be recycled to the regeneration process. When physical separation ofthe resin bed in this manner is used, the rinse water need not satisfythe stringent purity level described above; the regenerated resin isallowed to suffer local contamination and the contaminated top layer issimply separated; and preferably retained to be added in to the nexttank for regeneration. The lower portion of the bed would besubstantially free of ions and ready for filling into bottles.

Such embodiment is equivalent to a final polish of the input rinse downwater. The portion of resin subject to contamination may therefore beloaded into a first rinse tank, the remainder loaded into a second suchtank and the rinse down water then passes through the first tank, theeffluent therefrom flowing into the second tank.

In accordance with another aspect of the invention, physical separationof contaminated regenerated resin may also be achieved by providing aphantom stratum or pre-layer of resin ahead of the regenerated bed, orregenerated and mixed bed, to capture the ionic load of the rinse water.The phantom pre-layer is preferably provided as a resin-filled cap,cartridge, bed, bottle or another vessel that fits in-line upstream ofor above the regenerated resin during a rinse operation, effectivelypolishing and/or re-polishing the intended rinse water before it reachesthe resin bed. Such a phantom stratum may have a considerably largervolume than the strata discussed above, and may serve for many regenbatches. The effluent leaving the stratum should be monitored forquality, and its resin replaced or regenerated long before breakthroughof weakly held species occurs. Such a phantom stratum arrangement isillustrated for a cylindrical tank 40 in FIG. 4B. The tank has a top orproximal end 41 and a distal or bottom end 43, with an outlet port atthe distal end. The pre-layer may be embodied as a cap or a cartridgestructure 45 that fits on top of the tank 40, and holds a bed,preferably at least several inches long along the direction of rinseflow, of regenerated resin 50. The bed depth may be less if finer sizeresin beads (such as employed for power plant condensate polishing) areused. The resin 50 may be identical to the resin 35 that is beingrinsed. However, cap structure 45 separates and secures the resin 50 inan upstream position, so that any ionic loading in the rinse water willbe entirely taken up by the resin 50 rather than the resin 35. Afterrinse, the cap is removed, and the tank or bottle (stage 208 or 209,above) is treated as before. The pre-layer may also be embodied in anin-line cartridge (illustrated) through which fluid is provided to thetop of the tank. The cartridge may be placed in the caustic path to theregeneration tank and thus be regenerated when not used for polishingrinse water.

Thus, physical separation of the potentially loaded layer will assurethat the regenerated remainder of the resin is suitably clean for UPWpolish applications, and the bottles of ion exchange resin refilled fromthe mixing tank will have long life and dependably low leakage of weaklyionic species. During the rinse to quality, the effluent of the resincolumn may be monitored for a boron endpoint to assure optimumsuitability of the regenerated beads. This data may also be used tomodify or control regeneration process variables. In water treatmentsystems having a boron monitoring on polish stages, one or more flowsmay be controlled based on detected boron leakage levels, or on boronconcentration and temperature.

It will be understood by those skilled in the art that varioussubstitutions or changes in elements may be employed in carrying out theinvention. Thus, rather than employing a detector between polishingunits, the invention may employ a probe that samples water from aposition between polishing units, or from an intermediate position ordepth of a polishing bed of resin or elsewhere. Similarly, while theinvention has been described in relation to conductivity and to weaklyionic silica and boron species captured in anion exchange resins,similar effects apply to cation exchange resins, and the inventioncontemplates corresponding precautions, changes in regenerationhandling, introduction of sacrificial or phantom resin strata in theflow path, and other effective counter measures to assure purity ofregenerated cation exchange resins.

The invention being thus disclosed and illustrative embodimentsdescribed, further variations and modifications within the scope andspirit of the invention will occur to those skilled in the art, and allsuch variations and modifications are considered to be within theinvention as defined herein and by the claims appended hereto.

The invention claimed is:
 1. A process for regenerating an ion exchangeresin, the process including displacing captured ions from the resin toregenerate its ion capture functionality followed by rinsing the resinto remove excess material, wherein the improvement comprises the step ofrinsing or otherwise contacting the resin with deionized water fromwhich boron has been excluded below a boron content of 1 ppb or less. 2.The process of claim 1, wherein boron is specifically excluded by thestep of providing a sacrificial layer of resin upstream of said ionexchange resin to capture boron present in rinse water.
 3. A process forregenerating an ion exchange resin, such process comprising the stepsof: regenerating an ion exchange resin thereby displacing captured ionsfrom the resin to regenerate its ion capture functionality; depositingthe regenerated resin in a tank to form a bed of regenerated resin;placing a bead-retaining structure below a top surface of the bed ofregenerated resin to form a to stratum of resin; applying deionizedrinse water in a downward direction to the top surface of the bed ofregenerated resin whereby the to stratum of resin is preferentiallycontaminated with boron; and removing the top stratum of resin from thetank after the step of applying the deionized rinse water to the topsurface of the bed.
 4. A resin regeneration process comprising the stepsof: regenerating an ion exchange resin thereby displacing captured ionsfrom the resin to regenerate its ion capture functionality; providing abed of the regenerated ion exchange resin; providing a pre-layer ofregenerated or virgin ion exchange resin; passing deionized waterthrough the prelayer of regenerated or virgin resin to exclude boronfrom the deionized water to a boron content of 1 ppb or less; passingthe deionized water having a boron content below 1 ppb through the bedof regenerated resin to rinse the resin; and maintaining the prelayerwithin a cap, cartridge, bed, bottle, or vessel that is spaced apartfrom the bed of regenerated ion exchange resin.
 5. The resinregeneration process of claim 4, further comprising the step ofregenerating the prelayer.